The mitochondrial cytochrome b-c1 complex is an important electron transfer complex in the mitochondrial bioenergetic apparatus. The purified complex is composed of 10 protein subunits and about 20% of phospholipids. There are two cytochrome b one cytochrome c one iron-sulfur cluster and one ubiquinone in the complex. The molecular weight was calculated to be 236,000 dalton. The complex was crystallized in PEG in the presence of heptantriol and detergent. The crystals were stable at cold temperatures and they diffract x-rays to about 7 w resolution using a laboratory source and area detector. The crystals diffract to 4.5 w using a synchrotron source and rotation camera. Our newly improved crystals diffract to 2.9 w the using synchrotron source and rotation camera at SSRL. We wish to collect a complete data set on native crystals and start to do some screening on heavy atom derivatives and solve the structure in two years.